Answer the following questions
(i) Which element of the first transition series has highest second ionisation enthalpy?
(ii) Which element of the first transition series has highest third ionisation enthalpy?
(iii) Which element of the first transition series has lowest enthalpy of atomisation?
(b) Identify the metal and justify your answer.
(i) Carbonyl `M(CO)_(5)`
(ii) `MO_(3)F`

Explanation

(i) The element copper (Cu) has the highest value of `Delta_(i)H_(2)` (1958 kJ `mol^(-1)`) because after losing 4s electron ( `3d^(10)4s^(1)` configuration ), `Cu^(+)` in acquires a stable electronic configuration. The release of the second electron from the ion is quite difficult.
(ii) The element zinc (Zn) has the highest value of `Delta_(i)H_(3)`(3826 kJ `mol^(-1)`). Its electronic configuration is `3d^(10)4s^(2)`. After losing two electrons, `Zn^(2+)(3d^(10))` acquire a stable configuration. The release of the third electron from the filled orbital is extremely difficult.
(iii) The element zinc (Zn) has the lowest value of enthalpy of atomisation (126 kJ `mol^(-1)`) because of the absence of any unpaired electron in its atom. Therefore, the metallic bonds in the crystal lattice are quite weak. It has, therefore, least enthalpy of atomisation value.